UI

List is in a tabular view, not in card view
Tabbed info in detail view.

Strengths

A lot of content - articles - with APIs linked to them.
Mashups.
Search works better because there is a lot more metadata.

Weaknesses

No automated filter. When you apply a filter, you need to click the search button (of an empty searchbox, in a different widget).
Some bugs (e.g. pagination, you can not remove sorting)
How are results sorted by default? Is there a quality algorithm?
No strong social aspect (followers data is not in the list)
No uptime - quality of the API?

Documentation is horrible. Sample codes and how-to's are simple articles.
E.g. The most popular API, first article links to a 2010 Not Found page:
http://www.programmableweb.com/api/google-maps/source-code
http://www.programmableweb.com/how-to/google-maps-api-javascript-get-local-search-results-google-source-code
http://www.webmonkey.com/2010/02/get_local_search_results_with_google_maps_and_a...